I. Technical Field
The present invention relates to a method and apparatus for reinforcing a structural member. More particularly, the invention relates to a composite, precast plastic insert for reinforcing a structural member which expands and may bond to the structural member when heated. The present invention further relates to the method of making and using the precast reinforcement insert.
II. Brief Description of the Background Art
Reinforcements for structural members used in the manufacture of vehicles and other objects formed of sheet metal have generally been metal parts that are welded in place. The metal parts used as reinforcements add weight, are expensive and add additional steps to the manufacturing process.
One attempt to eliminate the use of welded reinforcements is disclosed in U.S. Pat. No. 3,909,058 to Kramer wherein it is suggested that a structural part may be filled with a foamed plastic material. A disadvantage inherent in the use of foamed plastic as a structural reinforcement is that it is difficult to control the process sufficiently to assure accurate location of the reinforcement in a portion of the structural member. Also, the foamed plastic may be harmed by exposure to the hot temperatures encountered in use and in paint curing ovens used in modern automotive, appliance and other assembly plants. Structural foamed plastic generally is not intended to bond to the structural member but instead relies upon completely filling a cavity with foamed plastic which prevents the flow of air throughout the structural member, with the possible result of moisture being trapped within the structural member. Foamed plastic reinforcements are not generally as strong or crush resistant as metal reinforcements.
Another approach to reinforcing a hollow structural member is disclosed in U.S. Pat. No. 4,405,543 to Murphy which suggests packing a cavity in a part to be filled with a loose thermoset material including glass microbubbles or phenolic microballoons. The loose thermosetting material is packed into the part and cured in the final part into a low density, fused solid mass. Such a process is inappropriate for use in assembly line operations because the material must be packed into the part, or structural member, to be filled by special presses.
Applicant's copending application, Ser. No. 674,226, filed Nov. 23, 1985 and now U.S. Pat. No. 4,610,836, and entitled "Method and Apparatus for Structural Reinforcement", discloses a structural reinforcement comprising a cloth impregnated with a low temperature cure, one-part epoxy and is coated on one face with a high temperature cure one-part epoxy. The cloth may be stamped and plastically deformed to fit within the confines of a structural member and filled with glass macrospheres which are coated with a low temperature curing adhesive. Subsequent heating of the structural member in a paint oven cures the high temperature epoxy, bonding the macrospheres to the epoxy-coated cloth and to each other to reinforce the structural member.
In another embodiment disclosed in Applicant's copending application, glass microspheres coated with an adhesive are blown in particulate form, as loose pellets, into a hollow structural member and positioned within the structural member by means of baffle plates positioned in the hollow structural member. Another concept disclosed in the application is partially filling the structural member with a heat vaporizable material, such as styrofoam pellets, then filling an adjacent portion of the structural member with the loose adhesive-coated macrospheres in the region which requires reinforcement. The heat vaporizable material is then vaporized by the heat of the paint curing oven while the adhesive-coated macrospheres are cured in place. Applicant's prior work resulted in a reinforcement which uses glass microspheres to reinforce a structural member without preventing air flow therethrough. In some instances, it is desirable to provide a reinforcement which prevents air flow through the structural member.
The present invention provides an improved reinforcement, a new, simplified method of making composite precast reinforcement inserts and a new method of using such inserts as high strength, crush-resistant reinforcements of structrual members which do not require special tooling.